1. Field of the Invention
The present invention relates generally to golf balls, and golf ball mantle layer and cover materials. More particularly, the present invention relates to multi-layer golf balls having mantle layer materials composed of cast urethanes and cover materials composed of injection moldable materials.
2. Description of the Related Art
Conventionally golf balls are made by molding a cover around a core. The core may be wound or solid. A wound core typically comprises elastic thread wound about a solid or liquid center. Unlike wound cores, solid cores do not include a wound elastic thread layer. Solid cores typically may comprise a single solid piece center or a solid center covered by one or more mantle or boundary layers of material.
Materials previously used as golf ball covers include balata (natural or synthetic), gutta-percha (natural), and ionomeric resins (e.g., DuPont's Surlyn.RTM.).
Balata is, typically, the benchmark cover material with respect to click (i.e., the sound made when the ball is hit by a golf club) and feel (i.e., the sensation imparted to the golfer when hitting the ball). Upon impact, the soft and flexible balata covers compress against the surface of the golf club, producing a good "click and feel." Consequently, experienced golfers are able to apply a spin to control balata covered golf balls in flight in order to produce a draw or a fade, or a backspin which causes the ball to "bite" or stop abruptly on contact with the green. Although balata provides golf balls with good playability properties, it is expensive compared to alternative materials. In addition, golf balls covered with balata tend to have poor durability (i.e. poor cut and shear resistance). Balata covered Golf balls, therefore, tend to have a relatively short life span.
As compared to balata, ionomeric resins are typically less expensive and tend to have good durability, but typically have poor click and feel. This is because although the ionomeric resins are very durable, they tend to be very hard when used for golf ball cover construction. In addition, because ionomeric resins are harder than balata, the ionomeric resin covers do not compress as much against the golf club upon impact, thus producing less spin. The "hard" ionomeric resins, however, provide golf balls with good distance.
Therefore, a great deal of research continues in order to develop a golf ball cover composition exhibiting not only the improved impact resistance and carrying distance properties produced by the "hard" ionomeric resins, but also the playability (i.e., "spin," "click and feel," etc.) characteristics previously associated with the "soft" balata covers, properties which are still desired by the more skilled golfer.
Particularly, polyurethanes have been proposed as golf ball cover materials. Polyurethanes are the result of crosslinking a prepolymer by reacting it with a polyfunctional curing agent, such as a polyamine or a polyol. A prepolymer is the reaction product of, for example, a diisocyanate and a polyol (e.g., a polyether or a polyester).
Some polyurethanes are thermoset, i.e., a substantially irreversibly set polymer, and others are thermoplastic, i.e., recyclable. Several patents describe the use of polyurethanes in golf balls.
Gallagher, U.S. Pat. No. 3,034,791 describes a polyurethane comprising the reaction product of poly(tetramethylene ether) glycol and 2,4-toluene-diisocyanates (TDI) (either pure or an isomeric mixture).
Dusbiber, U.S. Pat. No. 4,123,061 describes a polyurethane comprising the reaction product of a polyether (i.e., polyalkylene ether glycol, e.g., polytetramethylene ether glycol) and a diisocyanate (e.g., 2,4-toluene diisocyanate (TDI), 4,4'-diphenylmethane diisocyanate (MDI), and 3,3'-dimethyl-4,4'-biphenylene diisocyanate (TODI)) and a curing agent having at least two reactive amine groups (e.g., triisopropanol amine and trimethylol propane).
Hewitt, et al., U.S. Pat. No. 4,248,432 describes a thermoplastic polyesterurethane as a reaction product of a polyester glycol (molecular weight of 800-1500) (aliphatic diol and an aliphatic dicarboxylic acid) with paraphenylene diisocyanate (PPDI).
Kolycheck, U.S. Pat. No. 4,442,282 describes a thermoplastic polyesterurethane made by reacting a 1,12-dodecandioc acid polyester (molecular weight of about 1500-5000) with MDI.
Wu, U.S. Pat. No. 5,334,673 describes using a polyurethane prepolymer cured with a slow-reacting curing agent selected from slow-reacting polyamine curing agents and difunctional glycols.
Furthermore, two patents specifically describe multi-layer golf balls having a mantle layer which may comprise polyurethane material.
Cavallaro, U.S. Pat. No. 5,688,191 describes a multi-layer golf ball which has a mantle layer composed of a dynamically vulcanized thermoplastic elastomer, functionalized styrene-butadiene elastomer, thermoplastic polyurethane or metallocene polymer or blends thereof. Preferably, the mantle layer comprises a thermoplastic polyurethane. Further, Cavallaro discloses that the mantle layer is compression or injection molded over the core, and must withstand the temperatures applied during the application of the cover layer.
Similarly, Sullivan, U.S. Pat. No. 5,803,831 describes a multi-layer golf ball which, in an alternative embodiment, includes an inner cover having a greater shore D than the outer cover which may optionally comprise thermoplastic polyurethane, such as various Estane.RTM. products available from B. F. Goodrich.
In addition, several patents describe forming polyurethanes using PPDI.
Kolycheck, U.S. Pat. No. 5,159,053 describes a thermoplastic polyurethane having electrostatic dissipative properties, an average molecular weight of about 60,000-500,000, and comprising a hydroxyl terminated ethylene ether oligomer glycol intermediate (i.e. a polyethylene glycol) reacted with a non-hindered diisocyanate (e.g. PPDI, MDI, NDI, XDI, CHDI) and an extender glycol to produce a high molecular weight thermoplastic polyurethane.
Ohbuchi, et al., U.S. Pat. No. 5,066,762 describes a thermoplastic polyurethane resin obtained by reacting a PPDI, hydroxyl terminate poly(hexamethylene carbonate) polyol (molecular weight 850-5000) and a short chain polyol as an extending agent. Asserted improvements are in hydrolysis resistance, heat deterioration resistance, temperature dependency and compression set.
Kolycheck U.S. Pat. No. 5,047,495 describes a polyurethane reinforced fabric molded flexible fuel tank made of a high molecular weight thermoplastic polyurethane polymer binder (molecular weight 60,000-500,000) comprising the reaction product of an ethylene ether oligomer glycol intermediate (a hydroxyl terminated diethylene glycol aliphatic linear polyester, or a polyethylene glycol) and a non-hindered diisocyanate (PPDI, MDI, XDI, CHDI) and an extender. The material is said to exhibit good fuel resistance.
None of these polyurethanes have proven satisfactory for use in golf balls or, more particularly, as mantel layer materials for multi-layer golf balls. For example, prior multi-layer balls tend to have softer cover layers and, thus, not sufficiently abrasion resistant. Furthermore, thermoplastic polyurethanes with reinforced fabric, as possibly suggested by Kolycheck, should not be used in golf ball materials because such an addition would lower those physical properties of the thermoplastic which are desirable for golf balls.